The following summary describes four projects that attempt to investigate, at the molecular level, the roles a number of regulatory molecules, including, A kinase, kinesin light chains, the modulatory neuropeptides buccalin and myomodulin and rab 3 proteins, play in neural function. Two different invertebrate systems are currently being studied. Synaptic plasticity is being studied as a consequence of changes in the distribution and substrate specificity of A kinase catalytic subunits in response to the application of extracellular stimuli to sensory neural clusters in the sea hare Aplysia californica. Secondly, we have characterized the peptide families of buccalin and myomodulin in an attempt to gain further insights as to how peptide families collectively contribute to pre- or postsynaptic neuromodulation. The molecular characterization of peptide receptors through which signal transduction cascades are activated to affect modulation, for example G protein coupled receptors, is also being actively pursued. The characterization of kinesin light chains in the squid Loligo pealei, is being undertaken to define the diversity of light chains in the nervous system and ultimately to determine function and specificity with regard to intracellular transport, particularly axonal transport in neurons, of membrane-bound organelles. Similarly, cloning of the small GTP-binding proteins is being pursued to determine the role rab 3a, in particular, plays in synaptic transmission. Although each project is being studied independently, there are aspects of each that directly impinge on another. For example, the effects of myomodulin are believed to be affected through the activation of the A kinase cascades. It is also believed that the activity of kinesin, both heavy and light chains, are regulated via phosphorylation in which A kinase is a likely candidate. The synaptic vesicles that buccalin, myomodulin and rab 3a localize to are carried along the axon via fast axonal transport, a mechanism thought to be facilitated by kinesin.